Breast cancer is the second leading cause of cancer deaths in women and is the most common cancer among women. The primary cause of death in breast cancer is metastasis, a process that is still poorly understood, and it is still not possible to accurately predict the risk of metastasis formation in patients. The specification of cell fate occurs through the establishment of hierarchical networks of transcription factors. We have shown that GATA-3 plays a fundamental role in the maintenance of the luminal cell fate in the adult mammary gland and that GATA-3 may be playing a causal role in the pathogenesis of luminal mammary cancer. In the parent grant, we are testing the hypothesis that GATA-3 maintains the differentiation of breast neoplasms, and that its loss plays a causal role in malignant progression. We have now identified Zeppo1 (Znf703) and Zeppo2 (Znf503) as novel zinc finger genes downstream of GATA-3 regulation. Importantly, Zeppo1 is a gene in the amplicon on chromosome 8p11-12 is present in ~25% of human breast cancers and is associated with increased cell proliferation and tumor grade, and a reduction in metastasis-free patient survival. In this competitive revision, we propose to stimulate the economy through job creation to accomplish the new scientific objective of determining the mechanism of action of Zeppo1. We propose to determine the mechanism of action of Zeppo1 as a regulator of cell adhesion, migration and polarity in mammary epithelial cells, by overexpressing or knocking down Zeppo1 in three- dimensional organotypic cultures of normal and tumorigenic mouse mammary epithelial cells and examine cell-cell adhesion, polarity and cell migration. We will determine whether Zeppo1 overexpression increases metastases in a mouse model of breast cancer. These studies will accelerate the understanding of the transcriptional regulation of tumor metastasis by providing significant, new insights into genes that affect processes later in progression than the loss of GATA3. By enabling the hiring of additional scientific staff, these competitive revision funds will facilitate studies that are amenable to investigation within the two-year funding period. . PUBLIC HEALTH RELEVANCE: Breast cancer is the second leading cause of cancer deaths in women and is the most common cancer among women. This study addresses an important aspect of women's health, that of how Zeppo1, a gene amplified in human breast cancer regulates breast tumors progression and metastasis. If we could prevent the increase of Zeppo1 or inactivate it in metastasizing tumors we would greatly improve breast cancer outcome and save the lives of millions of women. These studies may form the basis of intervention and therapy in breast cancer, potentially preventing breast cancer lesions from metastasizing.